1. Technical Field
The present invention relates to a spectral characteristic calculating device configured to calculate a spectral characteristic of an arbitrarily selected pixel of an image represented by digital image data obtained by electronic endoscopes.
2. Related Art
It has been known that a healthy area and an involved area exhibit different spectral characteristics. For example, an involved area has a greater reflection ratio than a healthy area for light having a predetermined wavelength range. Making use of the spectral characteristic, it is suggested a diagnostic method for judging whether a target area includes an involved portion or not based on the spectral characteristic of an endoscopic image of a human body cavity. According to the above diagnostic method, typically, a spectrometer is coupled to a fiber scope to obtain the spectral characteristic with respect an arbitrary portion of the target area of the human cavity. Alternatively, a fiber bundle is inserted through a treatment instrument channel of an endoscope, and the spectrometer is connected to the fiber bundle at the proximal side thereof.
As above, in a conventional technique, when the diagnosis is done based on measurement of spectral characteristics, it is necessary to use a spectrometer separately. As an alternative, there is suggested a method for evaluating the spectral characteristic without using the spectrometer. An example of such a method is disclosed in Evaluation and Analysis of Digital Color Image, Chapter 10, Estimation of Spectral Reflectivity and Its Application, Yoichi Miyake, Tokyo University Publication. In the above publication, an image of the human cavity is obtained and a spectral characteristic is calculated based on brightness information of an arbitrary pixel of the image represented by the image data.
Generally, an image data obtained by an electronic endoscope is represented by brightness values of three primary colors, RGB (Red, Green and Blue). A wavelength range of the R component is 550 nm-700 nm, a wavelength range of the G component is 450 nm-600 nm and a wavelength range of the B components is 300 nm-500 nm. As described above, each color components has a relatively wide wavelength width (i.e., 100 nm-150 nm). Meanwhile, what is required in the spectral diagnosis is a brightness (reflectivity) with respect to light having a relatively narrow range (e.g., about 10 nm width). Due to the difference of the wavelength width therebetween, typically, measured spectral data for light having a narrower range is estimated based on the RGB brightness values of the target area.